Various curing agents are known in the art for use in epoxy resin systems, such as aliphatic polyamines, polyamides, amido-amines, cycloaliphatic amines, certain anhydrides, phenol-formaldehyde, urea-formaldehyde, melamine-formaldehyde and aromatic amines.
Aromatic diamines have been in use for many years as curing agents for epoxy resins. They were originally introduced to increase the glass transition temperature (Tg) of the cured resins in order to impart increased dimensional stability at elevated temperatures In addition, aromatic diamines have been found to provide long pot lives. The cured epoxy resins produced using aromatic diamines have good physical properties and good resistance to solvents and chemicals.
The aromatic diamines most widely used for curing epoxy resins are m-phenylene diamine (MPD), methylene dianiline (MDA) and diaminodiphenylsulfone (DADS). Recently, however, MDA and MPD have come under an increasing attack due to their high toxicity. In fact, MDA has been found to produce cancer in laboratory rats. Accordingly, a need has arisen for new aromatic diamines which can serve as replacements for MDA without causing detrimental effects in the epoxy resins produced.
It has now been found that DAIPB blended with ATBN is a good curing agent for producing a rubber toughened epoxy resin having good tensile properties. The tensile strength achieved through the use of the DAIPB/ATBN blends is better than that achieved when using DAIPB alone.